There is a nice book of Alan Kramer, Dynamic of destruction: Vulture and Mass Killing in First World War, 2007, from which further useful notes can be extracted.
I would also browse through films: www.europeanfilmgateway.eu/ and
WWI Poetry Digital Archive, at: http://www.oucs.ox.ac.uk/ww1lit/gwa/
I'm currently a member of the UWS Digital Humanities Research Group.
Perhaps - see my attached PDF here, if it helps...(?)
It may give you ideas for approaches.
As - one (potential) way is, you could use a Digital Humanities method - and do a Google NGram search, on certain words that you believe, reflect French emotional reactions at that time. eg Words like: "Fear" "Terror" "Crime" "Criminal" "Reprobate" and maybe even "Sacre Bleu!" and "Merde!" (I am kidding with the last 2 words ;)
And - on the other hand - just to play "Devil's Advocate":
Is this really a good idea/approach though..? (ie - Isn't it speculation, and perhaps drawing a long bow?)
Hasn't, say, Prof David Bordwell (eg, in his excellent `Poetics of Cinema', 2008, and other places) convincingly showed (along with, EH Gombrich, Karl Popper, and Colin Martindale 1990 "The Clockwork Muse", etc) that `cultural reflectionist' theories are all: totally flawed? ie Wouldn't that be being "Fooled By Randomness" as Nassim Taleb would say?
I would suggest `disciplinary zeitgeist' in film (in France, but also in world cinema) rather than any cultural zeitgeist would be a better explanation...?
But if you decided it was a good idea, as I say you could use a Google Ngram study. It might provide some evidence for emotions in France at that time. But I'm currently quite skeptical however - because I am not convinced that culture (eg movies) reflect the state of society. But - maybe you can convince me! Or, maybe, someone can.
I would suggest to have a look at the work of Stéphane Audoin-Rouzeau and Annette Becker, who have explored the French society and multiple aspects such as religion, war enthusiasm, etc... A few of their books have been translated in English.